The present invention relates to flame retardant polyester and polyesterether compositions which have significantly reduced blooming of the flame retardant after molding, high temperature processability, reduced smoke generation, and superior heat aging.
Thermoplastic polyesters and polyesterethers have become increasingly important in recent years due to their excellent processability and superior mechanical, chemical and electrical properties. Exemplary of such thermoplastic polyesters is poly(butylene terephthalate) (PBT), which is prepared by the reaction of 1,4-butanediol and dimethyl terephthalate. PBT is commercially available from a variety of domestic and foreign sources. The physical properties of PBT, such as tensile and flexural strength and heat deflection temperature, are significantly enhanced by the addition of fiberglass to the composition.
A representative thermoplastic polyesterether is Hytrel.RTM., which is manufactured and sold by the duPont Company. This material is a copolyester which is prepared by the reaction of dimethyl terephthalate, polyether glycol, and excess 1,4-butanediol. Hytrel.RTM. is an elastomer which has superior tensile and flexural strength, abrasion resistance, and good electrical properties.
Many commercial uses for thermoplastic polyesters and polyesterethers require a level of flame retardancy not present in the base resin. Such compositions are desired for applications such as in home construction, automobile and air craft manufacture, packaging, electrical equipment, and the like. To meet this demand, a wide variety of halogenated compounds have been used in these compositions to impart flame retardancy. Unfortunately, however, the addition of flame retardants to the resin has been at the expense of other physical properties which render the resin desirable, such as superior toughness and strength. Specifically, the use of conventional flame retardant additives can cause decreased flexural strength and heat distortion resistance, particularly in glass filled compositions. Accordingly, a flame retardant additive must be carefully selected not only on the basis of its principal function, i.e. flame retardancy, but also with regard to its effect on the other physical properties of the polymer composition.
Many widely used flame retardants for PBT resin compositions, such as decabromodiphenyl ether, have a tendency to migrate to the surface of the molded article. This tendency, known as "blooming", represents a physical loss of the flame retardant from the molded article and can result in a breakdown in the surface electrical characteristics of the molded part. See U.S. Pat. No. 4,373,047 which discusses this phenomenon and discloses the addition of an olefin polymer or copolymer to such compositions in order to reduce blooming of the flame retardant.
The high processing temperatures required for molding thermoplastic polyester and polyesterether compositions also place constraints on the flame retardant additive which can be employed. Such processing temperatures are required to reduce cycle times, but often preclude the use of thermally unstable additives. Thermal instability can result in a deterioration in surface appearance as evidenced by an unsatisfactory color change in the molded article.
It is also highly desirable to further improve upon other physical properties of the composition such as smoke generation and heat aging.
Chlorinated bisimides such as those of the present invention have been disclosed as effective flame retardant additives for various polymers such as ABS and polyolefins. See, for instance, the disclosures in U.S. Pat. No. 4,374,220, issued Feb. 15, 1983, U.S. Pat. No. 3,877,974, issued Apr. 15, 1975, U.S. Pat. No. 3,734,758, issued May 22, 1973, and British Published Application No. 1,287,934, published Sept. 6, 1972. However, none of these references discloses the use of the chlorinated bisimides of the present invention as flame retardants in thermoplastic polyesters or polyesterethers. Moreover, none of these references suggest that the incorporation of such chlorinated bisimides in these resins would also reduce or eliminate blooming, reduce thermal degradation under high temperature processing conditions significantly reduce smoke generation, and provide better heat aging.
It is therefore a principal object of the present invention to provide superior non-blooming, flame retardant thermoplastic polyester and polyesterether compositions which possess excellent processability and physical properties.